This invention relates generally to an axle driving apparatus and, more particularly, to an assembly used in connection with a return to neutral mechanism adapted to be mounted to the housing of a hydraulic drive apparatus such as an integrated hydrostatic transaxle (“IHT”) or hydrostatic transmission (“HST”). The mechanism disclosed herein could also be used with hydraulic pumps or other types of hydrostatic transaxles.
The general design of IHTs and HSTs are known in the art and generally include a rotating hydraulic pump and a rotating hydraulic motor, carrying a plurality of reciprocating pistons which are in fluid communication through hydraulic porting. Rotation of the hydraulic pump against a moveable swash plate creates an axial motion of the pump pistons that forces an operating oil through the hydraulic porting to the hydraulic motor to move the motor pistons and cause rotation of the hydraulic motor to drive an output shaft or axle.
The swash plate position is adjustable to vary the speed and direction of rotation of the hydraulic motor and, accordingly, the speed and direction of the output rotation. For use in changing the position of the moveable swash plate, it is known to include a trunnion arm coupled to the swash plate. A speed change lever or a speed change pedal is, in turn, coupled to the trunnion arm through a wire or other driving link. In this manner, movement of the speed change lever/pedal results in movement of the trunnion arm to change the position of the swash plate to thereby control the speed and direction of the vehicle. An example of such a mechanism for adjusting the speed of a vehicle may be seen in commonly owned U.S. Pat. No. 6,122,996 which is incorporated herein by reference in its entirety.
For placing the swash plate in a position that neither affects the speed nor the direction of rotation of the hydraulic motor, i.e., the neutral position, a return to neutral mechanism is normally implemented as an integral part of the vehicle linkage. One known return to neutral mechanism is shown in commonly owned U.S. Pat. No. 6,782,797, the terms of which are incorporated herein by reference. Such a speed adjusting mechanism includes a return arm adapted to be mounted to casing in a fixed position indicative of a neutral position of the trunnion arm and a control arm that is mounted to and moves the trunnion arm. A pair of scissor return arms move the control arm in cooperation with the return arm for the purpose of moving the trunnion arm to the neutral position.